Pressure & Scuba Diving

Pressure is one of the physics topics for GCE O Level, sometimes the experiences you have gained in other areas is used in the classroom to make the teaching of physics more interesting. One such time was during the topic on pressure where my scuba diving experience and the theories learnt were used to embrace the topic.

Pressure is defined as force per unit area and is also expressed in PSI (Pounds per square inch), bar and atmospheres (ATM). We all know that pressure increases as you descend and decreases as you go higher. Have you wondered why dams have a larger base area (built slanted with a thicker base) and boiling takes a longer time at the peak of a mountain?

In diving, the surrounding pressure refers to the sum of air pressure and water pressure. At sea level the atmospheric pressure is about 1 bar (14.7 psi). This is the measure of the downward force on an imaginary 1 inch (2.5cm or 25mm) square colum from the top of the atmosphere to sea level (96km or 60 miles). As we know that water is denser than air, pressure increases when a diver enters the water and goes deeper, thus he experiences discomfort while entering and popping of the ears while ascending.

Our body comprises of 70% water that cannot be compressed but we have parts in our body that contains gases (sinuses, middle ears and lungs). When a diver enters the water, at 10m, where the body is under 1 atmosphiric pressure, Boyle's Law (by physicist Robert Boyle) takes place. As the depth increases to 10m, the pressure increases the the volume of your lung decreases by half. In order for a diver not to experience the squeeze (discomfort), he has to equalize his ears as he descends, this ensures that the pressure inside of the air spaces is equal to the pressure outside of the air spaces. Our eardrum is the wall between water and air. When the water pressure pushing on the outside of the eardrum is greater the the air presure from the inside, the diver experiences discomfort. That is why pinch shut our nose and descend as we blow gently into our nose. If halfway through there's any discomfort, just flip your legs, ascend to a comfortable depth, eaqualise then descend. I remember during the 3rd dive I couldnt get rid of the discomfort and had to stop descending. The discomfort lasted more than a week after I arrived in Singapore.